Multiple fracturing in a well



D. SCHELL ETAL.

MULTIPLE FRACTURING IN A WELL iN'vNToRs DWIGHT SCHELL IRMAL J WALLEN JAMES E. WILKES ATTORNEYS 2 Sheets-Sheet 1 II I Dec. 6, 1966 Filed Dec. 26,

1966 D. SCHELL ETAL MULTIPLE FRACTURING IN A WELL 2 Sheets-Sheet 2 Filed Dec. 26, 1965 United States Patent Oil-ice 3,289,762 Patented Dec. 6, 1%66 3,223,762 MULTIPLE FRACTURING IN A WELL Dwight flchell, Irrnal J. Wallen, and Iarnes E. Wilkes,

Indiana, Pa, assignors to Hallihurton Company, Duncan, Okla, a corporation of Delaware Filed Dec. 26, 1963, Ser. No. 333,363 8 Claims. (Cl. 166-35) This invention relates to hydraulic fracturing in a well and, more particularly, to a method for successively fracturing formations at two or more selected elevations in a well.

Fracturing a formation in a productive zone is often desirable, since it improves the drainage into the well. Several productive formations may be separated by unproductive formations and accordingly it may be desirable to fracture the productive formations, although they are at widely spaced elevations in the well. If multiple fracturing is attempted simultaneously, the position of the fracture cannot be controlled, since a greater pressure is required to initiate a fracture than to extend the fracture into the formation. This problem may be overcome, however, by temporarily plugging the well above the elevation of the formation which has already been fractured, so that the fracture will not absorb the fracturing fluid.

The advantage of fracturing in two or more zones is that it usually increases the rate of production from a well. The increased production, however, is obtained at the expense of conducting two or more separate fracturing operations. This may include the cost of a bridging plug between adjacent fracture zones and the cost of the rig time involved in drilling out a plug which separates two zones, if necessary. The methods previously proposed for temporarily plugging the well, therefore, are relatively expensive. Accordingly, it might not be economical to fracture an upper formation by the conventional techniques, since the extra expense involved would not be justified by the increase in production gained by fracturing the upper formation. However, if the cost of fracturing multiple stages is reduced substantially, then multiple fracturing would be carried out more often, thereby increasing the total production.

Accordingly, it is an object of this invention to provide an improved method for fracturing in multiple stages.

It is another object of this invention to provide a method for producing multiple fractures which requires a minimum of equipment and time.

It is a further object of this invention to provide a method for temporarily plugging a lower formation while fracturing the upper formation.

These objects are accomplished in accordance with a preferred embodiment of the invention by running tubing in a well with a baflle placed in the string, so that it may be positioned between an upper formation and a lower formation. The tubing is cemented in the well and the tubing opposite the lower formation is perforated by conventional methods. An open hole packer may be placed in the end of the tubing, if the lower portion of the well including the lower formation is an open hole. The casing is then cemented in above the packer and it is not necessary to perforate at the elevation of the lower formation. Fracturing fluid is flowed into the tubing for fracturing the lower formation. After the fracturing has been completed, a ball or plug is pumped down the tubing and lodges on the baflie, between the upper and lower formations. A perforating gun is lowered in the casing to perforate the tubing at the elevation of the upper formation. The upper formation is then fractured and, since the ball covers the opening in the baflie and isolates the lower formation from the fluid pressure above the baffie, the fracturing fluid is forced only through the perforations in the tubing opposite the upper formation. When the fluid pressure in the well is reduced, the fluid in the lower formation is under suflicient pressure to lift the ball off the baflle and to cause the ball to flow to the top of the tubing. Both the upper and lower formations may then produce at the same time.

This preferred embodiment of the invention is illustrated schematically in the accompanying drawings in which:

FIG. 1 is a cross sectional view of a well showing the step of cementing of the tubing in accordance with the method of this invention;

FIG. 2 is a cross sectional view of the well showing the step of fracturing the lower formation;

FIG. 3 is a cross sectional view of the well showing the step of fracturing the upper formation;

FIG. 4 is a cross sectional view of the well after the pressure is reduced in the well;

FIG. 5 is a cross sectional view of a well wherein the lower formation which is to be fractured in accordance with the method of this invention is an open hole;

FIG. 6 is a cross sectional view of the well in FIG. 5 showing the step of fracturing the lower formation;

FIG. 7 is a cross sectional view of the well in FIG. 5 showing the step of fracturing the upper formation; and

FIG. 8 is a cross sectional view of the well in FIG. 5 after the pressure is released on the well fluid.

The method of this invention may be employed when the portion of the well which penetrates the lower formation is either an open hole or is cased. The steps of the method are shown in FIGS. 1 to 4, as they are carried out in a well in which the hole is cased in the portion opposite both the upper and lower formations. Tubing 2 is run in a well bore 4. The tubing 2 has a baflie 6 placed in the tubing 2 and spaced sufliciently above the lower end of the tubing that it is positioned between the two formations to be fractured, as shown in FIG. 1. The lower end of the tubing 2 extends below the lower formation. A shut-off baffle 8 is secured to the lower end of the tubing 2 and a float shoe 10 is attached to the tubing below the baflle 8. In order to center the tubing 2 in the well bore 4, a conventional centralizer 12 is secured in the tubing string.

Cement 14 is pumped down the tubing 2, so that it flows out of the float shoe 10, at the bottom of the tubing, and upwardly through the annulus between the tubing 2 and the well bore 4. A top cementing plug 16 is run in the tubing between the cement and fracturing fluid 17. The opening in the baffle 6 is large enough to permit the plug 16 to pass through the fracturing baflle 6, but the opening in the shut-off bafile is smaller than the plug 16 and it lodges on the baflie 8 to prevent leakage of the fracturing fluid outwardly through the float shoe. A check valve in the float shoe It) prevents reverse flow of the cement 14 into the tubing.

As shown in FIG. 2, after the cement 14 has set, the tubing 2 is perforated by conventional perforating apparatus to form holes 18 in the casing adjacent the lower formation. Pressure is then applied to the fracturing fluid 17 to form a fracture 2%). After the lower formation is fractured, a ball or plug 22 is dropped in the tubing 2 and lodges on the baffle 6. The ball 22 prevents fluid pressure from being transmitted from the portion of the tubing 2 above the battle 6 to the portion of the tubing 2 below the baffle. The tubing 2 is then perfortaed adjacent the upper formation to form holes 24 in the easing 2. When pressure is applied to the fracturing fluid 17, it flows through the holes 24 and into the formation to form a fracture 26 in the formation, as shown in FIG. 3.

When the pressure of the fracturing fluid 17 in the tube 2 is reduced, the pressure of fluid in the formation adjacent the fractures 20 and 26 causes the fluid to flow into the tubing 2 through the respective holes 18 and 24 and to flow upwardly in the tubing with a sufficient velocity to carry the ball 22 upwardly through the tubing, as shown in FIG. 4. Both of the zones may then produce simultaneously.

If the casing is relatively small or, if the portion of the well adjacent the lower formation is to be an open hole, the method and apparatus shown in FIGS. 5 to 8 may be used. A tubing 28 having a centraliner 30 for centering the tubing in a well bore 32 is run in .the well. The tubing 28 has coupled thereto a fracturing baffle 34 spaced from the lower end of the tubing and an open hole packer 36 adjacent the lower end of the tubing. A perforated anchor pipe 38 is secured to the lower end of the tubing 28, below the packer 36. The tubing 28 is run in the well until the baffle 34 is positioned between the upper and lower formations to be fractured. The packer is then set, as shown in FIG. 5, and the well is cemented above the packer either by dumping the cement down the annulus behind the tubing, or conducting the cement through a small pipe 40 extending down the well along the outside of the tubing.

The lower fraction is then fractured by increasing the pressure in the fracturing fluid 41. The fluid 41 communicates with the lower open hole portion of the well 32 through the openings 42 in the anchor pipe 38. The increase in fluid pressure causes the enlargement of a fracture 44 in the lower formation, as shown in FIG. 6. After the lower formation has been fractured, a ball or plug 46 is dropped down the tubing 28 and lodges on the fracturing baifle 34, as shown in FIG. 7, to isolate the fracture in the lower formation 44 from the fluid pressure above the bafile 34. A perforating gun is lowered in the tubing 28 to perforate the tubing and the cement with a plurality of holes 48. A fracture 50 is then formed in the upper formation by increasing the pressure in the fracturing fluid 41.

When .the upper formation has been fracture-d, the fluid pressure in the tube 28 is reduced below the pressure of fluid in the formation surrounding the fractures 44 and 50. This reduction in pressure causes the fluid to flow from the formation tubing 28 with sufficient velocity to carry the ball 46 upwardly to the top of the tubing, as shown in FIG. 8. The fluid then flows from both the upper and lower formations simultaneously.

The plugs or balls 22 and 46 are formed of a material which is resistant to deterioration by oil, water, or other fluids occurring in the well, and the balls must have sufficient structural strength to withstand the high pressure encountered in the fracturing process. The balls may also be subjected to high temperatures while in the well, and therefore, the material of which they are made must be capable of withstanding these high temperatures without breaking or distorting. The balls should have a higher density than the fracturing fluid, so that they will fall 1 through the fluid in the tubing at a reasonably rapid rate,

but they should not be so dense that fluid flowing upwardly in the tubing cannot lift the balls to the top of the tubing. One satisfactory material out of which the balls or plugs may be made is a lamina-ted thermosetting filled plastic containing phenolic or melamine resins. One such material is produced by the Synthane Corporation under the trademark Synthane. The balls or plugs may be weighted to increase their fall rate through the tubing.

Although the method of this invention has been described for fracturing two formations, more than two fractures may be accomplished successively by repeating the steps involved in forming the second fracture. The size of the opening in each baffle between the successive formations must he graduated from the smallest size at the lower end of the tubing to the largest size at the upper end of the tubing. successively larger balls are dropped to cooperate with their respective baffles.

The particular advantages of this invention are that the driller saves the cost of a bridging plug which would otherwise be required to isolate the upper producing zone from the lower producing zone, while the upper zone is being fracture-d. Furthermore, no rig time is involved in retrieving the bridge plug or drilling out a plug, as the fracturing ball is blown out 'by the fluid in the well. Since the lower formation can be isolated quickly, merely by dropping a ball in the tubing, both formations can be fractured in a minimum of time. Furthermore, due to the great saving in equipment cost and time, in certain borderline situations, the upper zone may now be fractured in accordance with this invention, although it would have been uneconomical by prior art methods.

While this invention has been illustrated and described in one embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

We claim:

1. A method for treating an upper formation and a lower formation in a well comprising lowering tubing in the well, said tubing having a baffle therein spaced above the lower end of the tubing, positioning the baffle between said upper and lower formations, cementing the tubing in the well, fracturing the lower formation, perforating the tubing opposite the upper formation, fracturing the upper formation with a free plug placed on the baffle to block fluid pressure communication to the lower formation, said plug having been placed after fracturing the lower formation and before fracturing the upper formation, and reducing the fluid pressure in the tubing, whereby the free plug flows to the top of the tubing.

2. A method for treating an upper formation and a lower formation in a well according to claim 1 wherein the free plug has a density greater than the density of the fracturing fluid, but is sufliciently buoyant to be lifted by the fluid flowing upwardly in the tubing during production.

3. A method for treating an upper formation and a lower formation in a well according to claim 1 wherein the free plug is formed of a laminated, filled thermosetting resin.

4. A method for treating an upper formation and a lower formation in a well comprising in sequence lowering tubing in the well, said tubing having a baffle therein spaced above the lower end of the tubing, positioning the baffle between said upper and lower formations, cementing the tubing in the well, fracturing the lower formation, placing a free plug on the baffle to block fluid pressure communication to the lower formation, perforating the tubing opposite the upper formation, fracturing the upper formation, and reducing the fluid pressure in the tubing, whereby the free plug flows to the top of the tubing.

5. A method for treating an upper formation and a lower formation in a well comprising placing tubing in the 'Well with the lower end of the tubing being spaced above the lower formation, said tubing having a baflle secured therein and positioned between the upper and lower formations, cementing the tubing in the well adjacent the upper formation, fracturing the lower formation, depositing a plug on the baifle, perforating the tubing opposite the upper zone, fracturing the upper zone, and reducing the pressure in the tubing for flowing the plug to the top of the tubing.

6. A method for treating an upper formation and a lower formation in a well comprising placing tubing in the well, said tubing having a baffle therein positioning the :baflie between the upper and lower formations, cementing the tubing in the well adjacent the upper formation, fracturing the lower formation, depositing a free plug on the baffle to block fluid pressure communication with the lower formation, perforating the tubing opposite the upper formation, fracturing the upper formation, maintaining the pressure of the fluid above the plug at a pressure greater than the pressure of the fluid in the upper and lower formations while perforating and fracturing of the upper formation and reducing the pressure in the tubing for selectively flowing the plug to the top of the tubing.

7. A method for treating an upper formation and a lower formation in a well comprising placing tubing in the well, said.tubing having a baffie therein positioned between said upper and lower formations, said tubing having a packer adjacent the lower end thereof, setting the packer between the upper and lower formations, cementing the tubing in the well adjacent the upper formation, fracturing the lower formation, placing a free plug on the baffle to block fluid pressure communication with the lower formation, perforating the tubing opposite the upper formation. fracturing the upper formation and reducing the fluid pressure in the tubing, where-by the free plug flows to the top of the tubing.

8. A method for treating an upper formation and a lower formation in a well comprising placing tubing in the well, said tubing having a bafile therein positioned between said upper and lower formations, cementing the tubing in the well adjacent the upper formation and the lower formation, perforating the tubing opposite the lower formation, fracturing the lower formation, (placing a free plug on the 'baflle to block fluid pressure communication to the lower formation, perforating the tubing opposite the upper formation, fracturing the upper formation, and reducing the fluid pressure in the tubing, whereby the free plug flows to the top of the tubing.

References Cited by the Examiner UNITED STATES PATENTS 2,769,497 11/1956 Reistle 166--42.1 3,028,914 4/1962 Flickinger 166-42.l 3,032,104- 5/1962 OReilly 166-35 3,111,988 11/1963 Davis et a1. 16642.1

CHARLES E. OC'ONNELL, Primary Examiner.

D. H. BROWN, Assistant Examiner. 

1. A METHOD FOR TREATING AN UPPER FORMATION AND A LOWER FORMATION IN A WELL COMPRISING LOWERING TUBING IN THE WELL, SAID TUBING HAVING A BAFFLE THEREIN SPACED ABOVE THE LOWER END OF THE TUBING, POSITIONING THE BAFFLE BETWEEN SAID UPPER AND LOWER FORMATIONS, CEMENTING THE TUBING IN THE WELL, FRACTURING THE LOWER FORMATION, PERFORATING THE TUBING OPPOSITE THE UPPER FORMATION, FRACTURING THE UPPER FORMATION WITH A FREE PLUG PLACED ON THE BAFFLE TO BLOCK FLUID PRESSURE COMMUNICATION TO THE LOWER FORMATION, SAID PLUG HAVING BEEN PLACED AFTER FRACTURING THE 